Hyperlacticaemia in children with status asthmaticus. The Stewart approach

BACKGROUND

Patients with status asthmaticus (SA) frequently present with lactic acidosis (LA). Our goal is to identify the nature of this LA using the Stewart physicochemical model and to identify the independent factors associated with LA in children with SA.

METHODS

Analytical study of a retrospective cohort using a nested case-control design. Twenty-eight episodes of SA in 24 children were included. Patients admitted to a paediatric intensive care unit (PICU) for SA over a 9-year period were recruited consecutively. Data were analysed using the Stewart model and the Strong Ion Calculator. Data were analysed using descriptive statistics and regression models were fitted within the general linear model.

RESULTS

Hyperlacticaemia (Lact[mM/L] = 3.905 [95% CI = 3.018-4.792]) and acidosis (pH = 7.294 [95% CI = 7.241-7.339]) were observed in 18 episodes (15 patients; 62.5%). According to the Stewart model, acidosis was caused by a decrease in strong ion difference. Initially, pCO2 was high (pCO2[mmHg] = 45.806 [95% CI = 37.314-54.298]) but the net unmeasured ion (NUI) component was normal (NUI = -4,461 [95% CI = -3.51 to -5.412]), and neither changed significantly over the clinical course. There was no need to determine pyruvate, as the NUI was normal and the LA was type B (non-hypoxic, lactate/pyruvate < 25). We observed a correlation (P = .023) between LA and intramuscular epinephrine administered on arrival at hospital, but not between LA and the cumulative dose of nebulized salbutamol.

CONCLUSIONS

Most patients with SA presented LA. The Stewart model confirmed that LA is not hypoxic, probably due to sympathomimetic-related glycolysis.

Anion Gap as a Determinant of Ionized Fraction of Divalent Cations in Hemodialysis Patients

BACKGROUND AND OBJECTIVES

Circulating levels of anions that bind to magnesium and calcium are often altered in patients with CKD. However, it is unknown how these alterations affect the ionized fraction of magnesium and calcium.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

This cross-sectional study involved patients on maintenance hemodialysis and patients not on dialysis who visited the outpatient department of nephrology. We collected whole-blood samples to measure ionized magnesium and calcium concentrations. Adjusted anion gap was calculated as an integrative index of unmeasured anions.

RESULTS

A total of 118 patients on hemodialysis and 112 patients not on dialysis were included. Although the prevalence of hypermagnesemia defined by total magnesium was much higher in patients on hemodialysis than in patients not on dialysis (69% versus 12%; P<0.001), the prevalence of hypermagnesemia defined by ionized magnesium did not differ significantly (13% versus 18%; P=0.28). Among patients on hemodialysis with high total magnesium, 83% had normal or low ionized magnesium. Consequently, the mean ionized fraction of magnesium in patients on hemodialysis was significantly lower than that in patients not on dialysis (51% versus 63%; P<0.001). Similarly, the mean ionized fraction of calcium in patients on hemodialysis was lower than that in patients not on dialysis (55% versus 56%; P<0.001). In patients on hemodialysis who had a higher adjusted anion gap than patients not on dialysis (mean [SD]: 14.1 [2.2] versus 5.1 [3.1]), the ionized fractions of magnesium and calcium were inversely associated with the adjusted anion gap. Furthermore, the anion gap significantly improved predictions of ionized magnesium and calcium in patients on hemodialysis.

CONCLUSIONS

Anions that accumulate in patients on hemodialysis contribute to the lower ionized fraction of magnesium and calcium. Equations that incorporate the anion gap provide better predictions of ionized magnesium and calcium in patients on hemodialysis.

Urine Anion Gap to Predict Urine Ammonium and Related Outcomes in Kidney Disease

BACKGROUND AND OBJECTIVES

Low urine ammonium excretion is associated with ESRD in CKD. Few laboratories measure urine ammonium, limiting clinical application. We determined correlations between urine ammonium, the standard urine anion gap, and a modified urine anion gap that includes sulfate and phosphate and compared risks of ESRD or death between these ammonium estimates and directly measured ammonium.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

We measured ammonium, sodium, potassium, chloride, phosphate, and sulfate from baseline 24-hour urine collections in 1044 African-American Study of Kidney Disease and Hypertension participants. We evaluated the cross-sectional correlations between urine ammonium, the standard urine anion gap (sodium + potassium - chloride), and a modified urine anion gap that includes urine phosphate and sulfate in the calculation. Multivariable-adjusted Cox models determined the associations of the standard urine anion gap and the modified urine anion gap with the composite end point of death or ESRD; these results were compared with results using urine ammonium as the predictor of interest.

RESULTS

The standard urine anion gap had a weak and direct correlation with urine ammonium (r=0.18), whereas the modified urine anion gap had a modest inverse relationship with urine ammonium (r=-0.58). Compared with the highest tertile of urine ammonium, those in the lowest urine ammonium tertile had higher risk of ESRD or death (hazard ratio, 1.46; 95% confidence interval, 1.13 to 1.87) after adjusting for demographics, GFR, proteinuria, and other confounders. In comparison, participants in the corresponding standard urine anion gap tertile did not have higher risk of ESRD or death (hazard ratio, 0.82; 95% confidence interval, 0.64 to 1.07), whereas the risk for those in the corresponding modified urine anion gap tertile (hazard ratio, 1.32; 95% confidence interval, 1.03 to 1.68) approximated that of directly measured urine ammonium.

CONCLUSIONS

Urine anion gap is a poor surrogate of urine ammonium in CKD unless phosphate and sulfate are included in the calculation. Because the modified urine anion gap merely estimates urine ammonium and requires five measurements, direct measurements of urine ammonium are preferable in CKD.